A major problem in determining the tumor-specificity and clinical applications of carcinoembryonic antigen (CEA) is the close homology with other glycoproteins of the CEA gene family which are expressed by tumors. CEA is a glycoprotein with molecular weight of approximately 180 kD that is one of a family of genes that encode approximately 8-10 highly similar proteins. CEA has been used as a serum marker for tumors of the colon, breast, and lung. The high degree of structural and sequence similarity between members of the CEA gene family explains the immunological cross-reactivity seen among existing immunological reagents. (See Shively et al, 1985. CEA-related antigens: Molecular biology and clinical significance. CRC Crit. Rev. Oncol. Hematol. 2:355-399; Barnett et al, 1989. Carcinoembryonic antigens: Alternative splicing accounts for the multiple mRNAs that code for novel members of the carcinoembryonic antigen family. J. Cell Biol. 108:267-276.)
Two CEA family members which share epitopes with CEA are Normal Cross Reacting Antigen (NCA) and a set of proteins that contain membrane spanning and cytoplasmic domains called transmembrane-CEA (TM-CEA). We have isolated and sequenced the complete cDNAs coding for CEA, NCA, and multiple transcripts of TM-CEA and have produced transfectant cell lines which express these CDNAS. These are the subject matter of co-pending applications U.S. application Ser. Nos. U.S. Pat. No. 5,122,599, 231,741, and 249,922 and articles. Barnett et al suora; Barnett et al. 1988. Carcinoembryonic antigen family: characterization of cDNAs coding for NCA and CEA and suggestion of non-random sequence variation in their conserved loop domains. Genomics. 3:59-66; Kamarck et al, 1987. Carcinoembryonic antigen family: Expression in a mouse L-cell transfectant and characterization of a partial cDNA in bacteriophage lambda gt11. Proc. Natl. Acad. Sci. U.S.A. 84:5350-5354. "Transfectant murine cell lines that express TM-CEA, NCA, and CEA, as described in U.S. patent application Ser. No. 249,922, have been deposited with the American Type Culture Collection (ATCC), Rockville, Md., U.S.A. ATCC 9731, 9732, and 9733, deposited Jun. 1, 1988, express TM-CEA, NCA, and CEA, respectivley." Antibodies specific to CEA family member proteins would allow better and more sensitive assessment of the differential expression in various disease states.
U.S. Pat. No. 4,467,031, entitled "Enzyme-Immunoassay for Carcinoembryonic Antigen" relates to a sandwich enzyme immunoassay for CEA in which the first of two anti-CEA monoclonal antibodies is attached to a solid phase and the second monoclonal is conjugated with peroxidase.
U.S. Pat. No. 4,489,167, entitled "Methods and Compositions for Cancer Detection", describes that CEA shares an antigenic determinant with alpha-acid glycoprotein (AG), which is a normal component of human serum. The method described therein concerns a solid-phase sandwich enzyme immunoassay using as one antibody an antibody recognizing AG and another antibody recognizing CEA, but not AG.
EP 83303759, entitled "Monoclonal Antibodies Specific to Carcinoembryonic Antigen," relates to the production of "CEA specific" monoclonal antibodies and their use in immunoassay.
WO 84/02983, entitled "Specific CEA-family Antigens, Antibodies Specific Thereto and Their Methods of Use", is directed to the use of monoclonal antibodies to CEA-meconium (MA)-, and NCA-specific epitopes in immunoassays designed to selectively measure each of these individual components in a sample.
U.S. Pat. No. 4,818,709, entitled "CEA-family antigens, Anti-CEA antibodies and CEA immunoassay" describes antibodies specific to specific CEA epitopes and epitopes of CEA-cross-reactive antigens.
The references of the prior art do not disclose a method and reagents that can discriminate between CEA, NCA and TM-CEA gene family member proteins.